Automatic telephone system



NOVQ 4 a 1924s 1,514,240 B. D. WILLIS AUTOMATIC TELEPHONE SYSTEM Filed Dec. 5, 1919 2 Sheets-Shut 1 Barman/D. M11115.

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B. D. WILLIS AUTOMATI C TELEPHONE SYSTEM Filed Dec. 3, 1919 2 Sheets-Sheet 2 flu/EH1 UP Bernard DMIZ Z15.

Patented Nov. 4, 1924.

STATES. PATENT OFFICE.

BERNARD D. WILLIS, OF OAK PARK, ILLINOIS, ASSIGNOB. T0 AUTOMATIC ELECTRIC COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

AUTOMATIC TELEPHONE SYSTEM.

Application filed December 3, 1919. Serial No. 342,239.

To all whom it may concern:

Be it known that I, Bnnxano D. WILLIS, a citizen of the United States of America, and a resident of Oak Park. in the county of Cook and State of Illinois, have invented certain new and useful Improvements in Automatic Telephone Systems, of which the following is a specification.

My invention relates in general to automatic telephone systems, and has for its object the provision of means for limiting the time during which a subscriber can hold a trunk for his own exclusive use. operation of the system herein contemplated, when a trunk line is taken for use by a calling subscriber. the trunk is made busy and the use thereof is made exclusive for a certain definite time. after which the subscriber is given a signal and the busy condition is removed, whereby the trunk line is rendered accessible to other calling subscribers. Then if no other subscriber should attempt to take the trunk line, the subscriber first calling my still continue touse it as long as he desires, even though it is nonbusy but as soon as a second calling subscriber extends a connection thereto, the connection of the first calling subscriber is released.

lVhile my invention is applicable to any or all of the trunk lines in the well known trunking systems, it is particularly valuable in certain special cases, as where. for example, a certain group of trunk lines is inadequate to handle the traffic, and it becomes necessary to adopt some means of limiting the unrestricted use thereof. The adaptation of the invention to a situation of this kind will be described hereinafter, reference being had to the accompanying drawings, in which Figs. 1 and 2 are circuit diagrams, while Fig. 3 is a diagrammatic layout of a system embodying the invention.

Referring to Fig. 3, consider two exchanges, a main exchange and a branch exchange. The main exchange is an automatic exchange in which connections are established through the medium of automatic switches under the control of calling subscribers. Suppose. for example, that the subscriber at substation A desires to call the subscribers at substation A. The connection is established by means of the individual line switch C, a first selector such as the first selector D, a second selector such as the second selector In the E, and a connector such as the connector H- This is the usual and well known percentage trunking system. At the branch exchange from the branch exchange to the main exchange, the substation A may be connected with substation A as follows: jack J cord circuit 0, jack J, trunk line X, individual switch C first selector D, second selector E, and a connector H. The ringing selectors mentioned above are provided to handle calls in the other direction, and may be accessible.

from a certain level in a certain group of second selectors. A connection from substation A to substation A may then be extended by way of the individual switch 0, the first selector D, second selector E, ringing selector F, trunk line X, jack J, cord circuit 0, and jack P With the above general layout in mind it will be assumed that for some sufficient reason it is considered necessary to limit the holding time on the trunk lines when they are used for main branch calls. The specific means for accomplishing this is applied to the ringing selectors and its operation will now be described. In view of the well known character of the equipment used only suflicient of the circuits have been shown to enable the invention to be understood; and reference is made to the following patents as showing the state of the art; U. S. Patent to Keith, Erickson and Erickson, No. 815,321. U. S. Patent to Keith, Erickson and Erickson, No. 815,176. U. S. Patent to Lamb, No. 1,193,160. U. S. Patent to Powell, No. 1,308,553. United States Patent to Erickson, No. 1,330,019.

For the purposes of this ex lanation it will be assumed that the subscriber at substation A has extended a connection through.-

and a first and second selector to the ringing selector F, Fig. 1, the wipers of the second selector in use having established connection with the bank contacts 2, 3 and 4. The conductors of the calling-line are thus extended by way of bank contacts 2 and 3, trunk conductors 5 and 7, and normally closed contacts of the reversing relay 8 to the windings of the double wound line resition.

The selector F is now ready to respond to impulses. The calling subscriber will therefore operate his calling device and dial in accordance with the last digit in the number assigned to the branch exchange trunks with the result that a series of interruptions is produced in the circuit of the line relay 9. The line relay deenergizes a corresponding number of times and at each deenergization sends a current impulse through the slow act ng series relay 12 and the vertical magnet 20 to battery. By the operation of the vertical magnet the switch shaft is raised step by step until the wipers 21-23, inclusive,stand opposite-the bank level in which are located the terminals of the lines extending to the branch exchange. The slow acting relay 13 is energized in series with the vertical magnet, maintaining its armature 39 attracted throughout the Vertical movement of the switch, and at the first upward movement of the shaft completes a circuit which extends by way of the working contact of the said armature, the off-normal springs 52, and the winding of the stepping relay 14 to battery. The stepping relay 14 is energized, prepares a.circuit for the rotary magnet 19 at 'itsarmature ll, and at its armature 40 looks itself to the grounded release trunk conductor 6.

At'the end of the vertical movement of the switch the slow acting relay 13 is deenerg'zed, and'at the resting contact of armature 39 completes the circuit of the rotary magnet 19, thereby initiating the operation of selecting an idle trunk line. Upon energizing, the rotary magnet advances the wipers 21-23, inclusive, into connection with the first set of contacts in the level opposite which they were raised, and at the same time interrupts the locking circuit of the stepping relay 14 which thereupon deenergizes and breaks the circuit of the rotary magnet which in its turn deenergizes. The operation n'ow depends upon whether the test wiper 22 is in engagement with a grounded or nongrounded test contact. If the trunk line terminating in the first set of contacts is busy the test contact associated therewith will be grounded and a circuit will be completed. which extends from the grounded test contact by way of the test wiper 22, armature 46 and its resting contact, left hand interrupter contact of magnet 19, off normal springs 52, and the winding of the stepping relay 14 to battery. The stepping relay is therefore again energized with the result that the rotary magnet 19 is also energized again to advance the switch wipers into engagement with the next set of bank contacts. This operation will continue as long as the test wiper 22 continues to engage grounded or busy test con tacts As soon as a nongrounded test contact is reached, which we will assume to be the test contact 25 associated with the trunk line X, the stepping relay 14 will not again be energized, but the switching relay 16 which heretofore has been short circuited,

will be operated by current flow in the following circuit: grounded release trunk conductor 6, contacts controlled by armature 27 of relay 8, conductor 6, winding of the switching relay 16, left hand interrupter contact of magnet 19, off normal springs 52, and the winding of the stepping relay 14 .to battery. The resistance of the switching relay 16 is so high that the stepping relay 14 is not operated. Upon energizing, relay 16 opensthe circuit of the vertical magnet at its armature 48, completes a circuit for the wiper switching relay 17 at its armature 47, and at its armature 46 completes a circuit over the test wiper 22 as follows: grounded release trunk conductor 6, contact springs controlled by armature 27, conductor 6, contact springs controlled by armature 35, working contact of armature 46 and the said armature, test wiper 22, .test

contact 25, winding of the switching relay 100 of the line switch C andv the winding of the stepping magnet of the said line switch to battery. By the closure of the above circuit ground potential is placed upon the test contact 25 and its multiples, the trunk line X is made busy to other calling subscribers, and also the switching relay 100 in the line switch C is energized to disconnect the trunk conductors from their normally closed connections in the said line switch. The relay 100 operates slightly before the relay 17 in the selector, the latter relay being made somewhat slow to energize by means of a copper slug. Upon the operation of the latter relay the line wipers 21 and 23'are connected at armatures-49 and 50,. respectively, anda signalling circuit is thereby established whereby ringing current from the generator Gen is projected out over the trunk 'line to operate the bridged relay 105 at the branch exchange.

The circuit extends by way of the resting contact of armature 45 and the said armature, armature 50 and its working contact, wiper 23, bank contact 26, line-conductor 102, contacts of key K, the condenser and upper winding of relay 105, upper contacts of relay 104, contacts of key K, line conductor 101, bank contact 24, line wiper 21, working contact of armature 49 and the said armature, armature 44 and its resting contact, and the upper winding of relay 15 to battery. The relay 15 does not respond to ringing current in the above circuit, but the relay 105 is operated, completes a looking circuit for itself, and closes the circuit of the lamp L which is lighted to signal the operator.

The connection, has now been extended to the branch exchange and a signal has been actuated at the operators position. When the operator observes the lighted lamp she will answer by inserting the left hand plug of her cord circuit 0 in the jack J at the same time throwing her key K to listening position. By the insertion of the plug in the jack the polarized relay 107, which is in series with the left hand winding of the repeating coil in the cord circuit, is bridged across the trunk conductors 101 and 102. As a result relay 15 at the ringing selector is energized, either by current from the generator Gen or by direct current from the battery associated therewith, thereby establishing a locking circuit for itself at its armature 43, and at armatures 44 and 45 closing the trunk conductors 5 and 7 through to the line wipers 21 and 23, respectively. The double wound relay 8 is now connected in bridge of the trunk line and is energized by current flow thereover. At armatures 28 and 29 relay 8 reverses the direction of current flow in the calling line in the usual manner, at armature 30 a circuit is completed for the magnet 75 of the time mechanism, and at armature 27 the release trunk conductor 6 is disconnected from conductor 6', and thelatter conductor is connected to ground by way of armature 27, armature 42 and its working contact, and off normal springs 53 and 54 to ground.

At the branch exchange, the operator may now obtain the desired number from the calling subscriber which in this case is the number of the subscriber at substation A and will then complete the connection by inserting the right hand plug of thecord circuit 0 in the jack J after which the key K will be thrown to ringing position for a moment. By this operation the cut-off relay associated with the line of substation A is energ zed in series with the sleeve relay 109 of the cord circuit, which latter relay causesthe illumination of the supervisory lamp L Although the relay 106 at the other end of the cord circuit is also energized over the sleeve of the cord the supervisory lamp L is not lighted because of the fact that the polarized relay 107 is energized in the proper direction to open its circuit. lVhen the called subscriber answers the double wound relay 108 will be operated and the lamp L will be extinguished.

The connection has now been established and the subscribers can converse as desired. In accordance with the invention, however, the time during which the calling subscriber can retain the trunk line for his own exelusive use is limited and the operation of the time mechanism will now be considered. As stated before, when relay 8 at the selector is energized a circuit is completed for the magnet 75 of the time mechanism. This mechanism is described fully in one of the publications previously referred to and will not be explained in detail herein. It will be sufficient to say that when the magnet 75 is energized the roller 77 which is constantly rotating in a counter clockwise direction begins to raise the plunger 76.

After a predetermined time which may be, for example; five minutes, the contact springs 78 and 79 are closed, thereby completing a circuit for the lower winding of relay 11. Upon energizing, relay 11 disconnects the test wiper 22 from the conductors 6' and completes a locking circuit for its upper winding as follows: ground at G upper winding of relay 11, armature 35 and its working contact, working contact of armature 46 and the said armature, test wiper 22, test contact 25, winding of relay 100, and the winding of the stepping magnet of line switchC to battery. The upper winding of relay 11 is of high resistance, not so high of course that the relay 100 wilLdeenergize, but sufiiciently high to reduce the ground potential on the test contact 25 to a point where the trunk line is made nonbusy. At its lower armature 36 relay 11 breaks the circuit of the magnet 75 of the time mechanism, thereby permitting the plunger 76 to restore, and at the same time removes the short circuit from the lower winding of relay 10, thereby causing this relay to energize in series with the line relav 9. Upon attracting its armature 32 relay 10 includes its upper winding in the circuit and at its armature 33 prepares a circuit for the release magnet 18. Also at armature 34 ground is disconnected from the original energizing circuit of the wiper switch relay 17, but this relay remains energized by reason of the alternative ground connection at armature 36 of relay 11. At

the same time that contact springs 78 and 79 were closed the contact springs 80 and 82 will be closed also. By this operation a circuit is closed for the secondary of the repeating coil forming "part of the signalling mechanism Q. The circuit may readily be traced from ground through the condenser in the said secondary winding, contact springs 81, 82 and 80, also lower winding of relay 9 and the lower winding of relay to ground. An audible tone is thus placed on the calling line which notifies the calling subscriber that the period of exclusiveuse has terminated and that he is liable to be disconnected at any time. The signal endures for only an instant; however, and the conversation may continue as long as desired subject only to the possibility of release by a second calling subscriber who may attempt to establish connection with the trunk line in use. If we assume that the conversation proceed without interruption until it ,is finished both subscribers will replace their receivers; Disconnection is accomplished in the usual manner which may be briefly explained as follows: By the replacement of the receiver at the calling station the line relay. 9 of the selector F 1s deenergized, thereby causing the deenergization of the release relay 12 which in turn I deenergizes to close the circuit of the release the usual manner to extend a connection to an idle first selector. The direction of cur rent flow over the trunk line is now reversed and the polarized relay 107 at the cord circuit O is operated in such a manner that. it will close the circuit of the supervisory lamp L The replacement of the receiver at substation A breaks the circuit of the relay 108 which therefore deenergizes to close the circuit of the supervisory lamp L The disconnect signals thus displayed indicate to the operator that the conversation is finished and she will pull down the connection. t

We will assume now that a second calling subscriber attempts to establish connection 4 with the trunk line X before the conversation just described-is finished. Ithas been previously stated that the trunk line is made nonbusy after a predetermined time by the substitution of ground through the upper high resistance winding of relay 11 for direct ground. Then the relay, corresponding to relay 14, of the second selector whlcn is being used by the second calling subscriber will not energize when the wipers of the selector ,makeconnection with the trunk line,

the rotation of the selector will cease and connection with the trunk line will be established 'is deenergized and a circuit is completed for the release magnet 18 as followsz ground at G armature 36 and its resting contact, armature 33 and its working contact, off normal springs 51 and the winding of the release magnet to battery. By the energization of the release magnet 18 the selector F t is restored to normal in the usual'manner and the connection of the first calling sub scriber with the trunk line X is broken. At the same time that the circuit of the release magnet is closed the circuit of the wiper switching relay 17 is opened and the wipers 21 and 23. are disconnected to prevent interference with other lines while the selector is returning to normal. When the connection is broken the calling subscriber will know that he can no longer use the trunk line to the branch exchange and he will replace his receiver, whereupon the remaining switches will be released. In case he has not finished his business with the subscriber I at the branch exchange he may again call the subscriber after waiting a reasonable length of time and in case an idle trunk line is found the connection may be reestablished as before; or in case none of the trunk lines are actually free but one or more are being held beyond the time limit, the calling subscriber will himself be in the position of the second calling subscriber previously referred to and will be able to take one of the trunk linesfor his own use arid release the connection of the subscriber who at that time is connected therewith.

Having fully described and ascertained the features .and aspects of my invention, what I consider to be new and desire to have protected by Letters Patent will be pointed out in the appended claims:

What I claim as my invention is:

1. In a telephone system, a trunk line, means including automatic switches whereby calling subscribers may extend connections over said trunk line, each connection being of unlimited duration unless another subscriber desires to use the trunk line, and means for limi ing the time during which any one subscriber may hold said trunk line exclusively for his own use so as to permit another subscriber to appropriate it for use at the end of a pre-determined time. I

2. In a telephone system, a trunk line, means includingautomatic switches whereby calling subscribers may extend connections over said trunk line, means reserving the trunk line to the exclusive use of the calling subscriber when a connection therewith has been established, and means for rendering the continued use of said trunk line non-exclusive after a predetermined time.

3. In a telephone system, a trunk line, means including automatic switches whereby calling subscribers may extend connections over said trunk line, means reserving the trunk line to the exclusive use of the calling subscriber when a connection therewith has been established, means for rendering the continued use ofsaid trunk line non-exclusive after a predetermined time, and means for terminating the use of said trunk line by the subscriber first calling when it is taken for use by a second calling subscriber.

4. In a telephone system, a trunk line, means including automatic switches whereby calling subscribers may extend connection-s over said trunk line, means reserving the trunk line to the exclusive use of the calling subscriber when a connection therewith has been established, means for rendering the continued use of saidtrunk line nonexclusive after a predetermined time, and means notifying the calling subscriber when the period of exclusive use is over.

5. In a telephone system, a line, means including automatic switches whereby calling subscribers may connect with said line, means for making said line busy when connection thereto is established, said busying means being effective to prevent any other connection from being extended to said line,

and means for automatically terminating the busy condition thereafter without releasing the connection.

6. In a telephone system, a line, means including automatic switches whereby calling subscribers may connect with said line, means for makin said line busy when connection thereto 1s established, means for automatically terminating the busy condition thereafter without releasing the connection, and means for releasing the connection when a second connection to said line is completed.

7. In a telephone system, a line, means including automatic switches whereby calling subscribers may connect with said line, means for making said line busy when connection thereto is established, means for automatically terminating the busy condition thereafter without releasing the connection, and means for; transmitting an audible signal to the calling subscriber to warn him that the connection is liable to be broken.

8. In a telephone system, a trunk line, a plurality of automatic switches having access to. said trunk line, means for making said trunk line busy when the same is seized by one of said switches, and means operated automatically after a predetermined time to render said trunk line non-busy prior to the disconnection of said switch.

9. In a telephone system, a trunk line, a plurality of automatic switches having access to said trunk line, means for making said trunk line busy when the sameis seized by one of said switches, means for rendering said trunk line non-busy after a predetermined time whereby it is again made accessible to the other switches, and means for releasing the switch first operated when the trunk line is seized by another of said switches.

10. In a telephone system, two exchanges, interconnecting trunk lines, automatic switches for use by calling subscribers in one exchange for extending connections over said trunk lines to the other exchange, busy circuit connections for rendering any trunk line inaccessible to other calling subscribers when it is taken for use, and means for altering said busy connections thereafter whereby the said trunk line is again rendered accessible to other calling subscribers without breaking the connection first established.

11. Ina telephone system, a trunk line, means including automatic switches whereby calling subscribers may extend connections over said trunk line, means for reserving the trunk line to the exclusive use of the calling subscriber when a connec- 13. In a telephone system, a line, means including automatic switches whereby calling subscribers may connect with said line, means for making said line busy when a connection has been 'establishd thereover, and time controlled means for automatically terminating the busy condition there. after while the connection is maintained.

14. In a telephone system, a line, means including automatic switches whereby calling subscribers may connect with said line, means for applying a busy potential to said line when connection thereto is established, and means for automatically switching the busy potential to a nonbusy potential without releasing the connection.

Signed by me at Chicago, Cook County, State of Illinois, this 28th day of November, 1919.

BERNARD n. WILLIS. 

